PHONON DIFFRACTION LIMITED PERFORMANCE OF FABRY-PEROT CAVITIES IN PIEZOELECTRIC EPI - HBARS

We report on phonon diffraction limited performance of GaN/AIN/NbN/SiC epitaxial HBARs (epi-HBARs) that act as Fabry-Perot acoustic cavities with parallel reflectors. In a series of devices with varying transducer diameter (phi), we find that the smallest epi-HBARs (phi=22.5 mu m on a 350 mu m thick substrate) are indeed limited by diffraction, yet achieve f x Q approximate to 10(12) Hz at 7.2 K. Near the diffraction limit, f x Q approximate to 10(14) Hz for phi >50 mu m, and for larger devices that are not diffraction limited, f x Q approximate to 2x10(16) Hz. We discuss the practical tradeoffs involved in using such high performance electrically transduced epi-HBARs compared to confocal HBARs with an engineered curved surface that are popular for phonon-qubit coupling in quantum acoustodynamic (QAD) systems.

Automated summary

This study investigates the phonon diffraction limited performance of GaN/AIN/NbN/SiC epitaxial HBARs and explores the tradeoffs in using them compared to confocal HBARs with curved engineered surfaces. The smallest epi-HBARs achieve high performance near the diffraction limit at 7.2K, while larger devices not limited by diffraction exhibit even higher performance.